Math.round() - JavaScript 编辑

The Math.round() function returns the value of a number rounded to the nearest integer.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

Syntax

Math.round(x)

Parameters

x

A number.

Return value

The value of the given number rounded to the nearest integer.

Description

If the fractional portion of the argument is greater than 0.5, the argument is rounded to the integer with the next higher absolute value. If it is less than 0.5, the argument is rounded to the integer with the lower absolute value.  If the fractional portion is exactly 0.5, the argument is rounded to the next integer in the direction of +∞.  Note that this differs from many languages' round() functions, which often round this case to the next integer away from zero, instead giving a different result in the case of negative numbers with a fractional part of exactly 0.5.

Because round() is a static method of Math, you always use it as Math.round(), rather than as a method of a Math object you created (Math has no constructor).

Examples

Using round

Math.round( 20.49); //  20
Math.round( 20.5 ); //  21
Math.round( 42   ); //  42
Math.round(-20.5 ); // -20
Math.round(-20.51); // -21

Specifications

Browser compatibility

BCD tables only load in the browser

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Number.toPrecision()
• Number.toFixed()
• Math.abs()
• Math.ceil()
• Math.floor()
• Math.sign()
• Math.trunc()